Understanding the ways that lymphocytes react to self antigens is a major goal of immunology research with implications for autoimmunity, lymphocyte development and the control of lymphocyte growth, survival, differentiation, and gene recombination. However, mechanistic studies have generally required the use of mouse models carrying randomly integrated or targeted antigen receptor transgenes, which distort lymphocyte development. One exception to this rule is work involving superantigens, which have been exploited to study many aspects of T cell biology without skewing or distorting normal T cell repertoire development. The hypothesis of this proposal is that custom superantigens can be generated and will be helpful to study, in a non-clonal immune system, the effects of self-ligands on B lymphocytes, or indeed other lymphocyte types. This hypothesis will be addressed through the following approaches. Single chain antibodies reactive to framework or constant regions of antigen receptor chains will be generated by engineering monoclonal antibody genes from hybridomas. These combining sites will be expressed as chimeric membrane proteins, called macroself antigens (Ags), in transgenic mice. Macroself Ag-expressing mice will then be used as adoptive recipients of normal bone marrow cells or analyzed directly for pertubations of lymphocyte survival, function, and receptor gene usage. Macroself Ag transgenics with specificity for IgM, Ig-kappa, IgD, and IgG2a allotypes will be generated, allowing analysis of immune tolerance in different cell compartments and developmental stages in a non-clonal immune system. These approaches will allow the analysis of central tolerance, peripheral tolerance, and tolerance in germinal center and memory cell compartments of otherwise normal mice. In addition, the utility of using macroself Ag mice as recipients of bone marrow or fetal liver to rapidly study the phenotypes of mouse mutants will be explored. [unreadable] [unreadable] [unreadable] [unreadable]